1. Field of the Invention
This invention relates generally to an enclosure assembly for one or more high frequency microelectronic circuits and, more particularly, to an enclosure assembly for one or more high frequency microelectronic circuits that includes a specially configured lead frame that is electrically connected to the circuits, and extends from the enclosure where a portion of the lead frame on the outside of the enclosure includes flared regions that are impedance matched to portions of the lead frame within the enclosure and to the input and output ports of the circuits.
2. Discussion of the Related Art
Currently, many applications exist for high frequency microelectronic integrated circuits operating in the GHz range, especially in conjunction with communication systems. As is well understood, high frequency signals are generally used in communication systems because these signals can be effectively transmitted at low power levels. For example, monolithic microwave integrated circuits (MMICs) have been extensively developed for use in applications such as cellular telephones, satellite receivers, personal communication systems, and remote sensing and control devices. Usually, these types of integrated circuits incorporate gallium arsenide (GaAs) devices including field effect transistors (FETs) and/or heterojunction bipolar transistors and associated circuitry that operate within the GHz frequency range.
In order to reduce power losses and protect these types of delicate integrated circuits against environmental conditions, it is generally a requirement that MMICs, as well as other related types of RF circuits, be packaged in some form of enclosure within a particular system. In order to meet the requirements of the industry, such an enclosure should not only protect the integrated circuit within, but also should be low cost and provide low losses at the operating frequencies of the circuit. Because improvements in the ability to produce low cost MMICs has significantly increased, traditional enclosures formed of one or more of metal, ceramic and plastic currently being used for this purpose have generally been unable to meet the price/performance requirements that are acceptable for the commercial microwave electronics market place. Therefore a need exists for a new low cost enclosure for this purpose.
When designing an enclosure for MMICs, it is necessary to consider impedance matching of a lead frame that connects the. MMIC to other integrated circuits in a particular system, such as power circuits and the printed circuit mother board, so as to reduce or eliminate transitional power losses of the signals between the various circuits. Impedance matching is particularly important for low power circuits so that the signals on the leads are not unnecessarily attenuated resulting in a reduced signal-to-noise ratio. For the types of MMICs discussed here, the MMIC, as well as the other integrated circuits and the mother board within the system, will generally have a characteristic impedance of 50 ohms. Because the MMIC is within an enclosure, the lead frame travels through different materials having different dielectric constants. A characteristic impedance exists for a particular lead frame with respect to the geometry of the lead frame, the distance between the lead frame and a ground plane and the dielectric material that exists between the lead frame and the ground plane. For example, the enclosure and the air outside the enclosure have different dielectric constants. Lack of satisfactory impedance matching at the transition regions between the different dielectric regions causes power losses in the signals being transmitted, as well as other types of effects such as reflective phenomenon. Therefore, different strategies are incorporated to match the characteristic impedance between the transition regions.
U.S. Pat. No. 5,376,909 issued to Nelson et al. discloses a package for an integrated circuit of the type described herein. Nelson et al. discuss providing impedance matching of a lead frame connected to the ports of the circuit at the location where the lead frame exits the package. The impedance matching is achieved by maintaining a predetermined relationship between a ground plane and the lead frame. Particularly, the width of lead lines of the lead frame are altered with respect to their spacing from the ground plane and the dielectric material between the lead lines and the ground plane.
The impedance matching of high frequency integrated circuits can be improved over the prior art. Further, the cost of a package encapsulating an MMIC circuit can be further reduced. It is therefore an object of the present invention to provide such improvements over known integrated circuit device packaging.